Remote monitoring systems are widely used e.g. for intruder and/or fire detection purposes. In a typical system a locally triggered alarm signal is relayed to the remote station where an operator can then alert the appropriate keyholder or emergency service. One of the problems with such a system is that of spurious triggering of the local detection resulting in false alarm signals. In an attempt to overcome this problem some workers have provided video monitoring of the surveyed premises. Such a technique is described for example in specification No. US-A-4,876,597. In that arrangement single video frames are digitally encoded and stored in a memory for subsequent viewing. There is now a need for more advanced systems that provide full video, e.g. real time video, monitoring of a remote location. However, current systems that provide this facility require the use of a high bandwidth data link, e.g. an ISDN or Magastream Line, to transmit the video signals to the monitoring station. This has restricted use of such a system to those locations where data transmission facilities are available.
It is an object of the invention to minimise or to overcome this disadvantage.
It is a further object of the invention to provide a remote surveillance system in which video signals may be transmitted over the public telephone network.